1. Field of the Invention
The present invention relates to scrubbing equipment used for a semiconductor device, and more particularly, to an automatic brush-height adjusting device for scrubbing equipment for cleaning a semiconductor wafer using a brush, in which the distance between the brush and the wafer surface is automatically adjusted using a laser.
2. Background of the Related Art
Production of semiconductor devices having microscopic structures requires high-precision technology. During processing, minute particles of dust on the circuits which constitute a semiconductor device may degrade the reliability of the finished semiconductor device. Even if dust contaminants produced during processing, which end up on a semiconductor wafer, do not adversely affect the circuit functions of the semiconductor device, they still may lead to fabrication difficulties. Therefore, the semiconductor device should be fabricated in a dirt-free environment, and the surface of the semiconductor wafer should be washed to remove minute particles of dust generated during processing.
The cleaning steps are carried out by sprinkling pure water on the wafer surface, or by allowing a rotary-fiber brush steeped in a cleansing agent or pure water to contact the surface of the wafer. Scrubbing equipment is used to clean the surface of the wafer by removing dust contaminants with a brush and pure water.
Recently available multilayer and high integration semiconductor devices are easily damaged. When the rotary fiber brush of the conventional scrubbing equipment contacts a wafer surface, films or patterns formed on the semiconductor wafer can be damaged. To prevent this problem, scrubbing equipment is used whose brush does not directly contact the wafer surface during the cleaning step.
When pure water is continuously sprinkled over the wafer surface, the surface of the wafer becomes covered with the pure water. At this point, the depth of the pure water on the wafer surface is about 1 mm to 2 mm. Then the brush is moved into the pure water, but not in contact with the wafer surface. A rotary chuck supporting the wafer begins to rotate, and the brush creates eddy currents in the pure water so that the minute particles are removed from the semiconductor wafer by the eddy currents.
Referring to FIG. 1, a conventional scrubbing equipment includes a rotary chuck 11 on which a semiconductor wafer 10 is placed, a brush arm 12 extending from shaft 13 at a right angle and fixed to the shaft 13 such that brush arm 12 can move up and down and rotate, and a brush 14 made of TEFLON and provided on one end of the brush arm 12. The brush 14 is housed in a slick cover to conceal the fibers forming the brush 14. In the cleaning step, an operator uses the naked eye to adjust the distance between the brush 14 and a wafer to be cleaned, based on the position of the tip of the brush cover.
When the scrubbing equipment is not in use, the brush 14 is placed in a pure water container 15 in order to prevent the brush 14 from drying out. A pure water nozzle 16 for pure water supply is provided over the rotary chuck 11. These components are controlled by a micro-controller 17.
Referring to FIG. 2, the operation of the scrubbing equipment will be described as follows.
When the scrubbing equipment starts to operate, a semiconductor wafer 10 is placed on the rotary chuck 11 and the rotary chuck 11 starts to rotate. Pure water is sprinkled over the rotating wafer 10. The shaft 13 supporting the brush arm 12 moves up and rotates so that the brush arm 12 also moves up and turns around the shaft 13. Then the brush arm 12 and brush 14 move down until the brush 14 is in contact with the pure water on the wafer 10. As the shaft 13 rotates, the brush arm 12 moves slowly in the direction of the arrow "b" in such a manner that the brush 14 moves parallel to the surface of the wafer until the brush reaches the center of the wafer.
As the wafer 10, which is fixedly mounted on the rotary chuck 11, rotates at high speed in the direction of the arrow "a", eddy currents are created by the brush 14 in the water on the wafer surface in the direction of the arrow "c", thereby performing the cleaning step for the removal of dust contaminants.
The pressure created by the brush is not important to the above-described scrubbing equipment. What is important is to maintain the appropriate distance between the wafer and the brush. In other words, if the brush is too far from the wafer and does not contact the pure water, or if the brush contacting the pure water generates weak eddy currents on the surface of the wafer, the cleaning efficiency is reduced. On the contrary, if the brush is too close to the wafer, the brush will scratch the wafer.
In the conventional scrubbing equipment, since the distance between the brush and a semiconductor wafer to be cleaned is adjusted with the naked eye on the basis of the position of the tip of the brush cover, when a worn-out brush is replaced by a new one, the height at which the brush is set must be readjusted by the operator.
When the conventional scrubbing equipment performs cleaning on various wafers of different film thickness, the distance between the brush and wafer should be readjusted for each film thickness. Therefore, the conventional scrubbing equipment may damage the semiconductor wafer being cleaned and cannot ensure the effectiveness of cleaning, and time is wasted during each readjustment.